Distribution and Cytoarchitecture of Sympathetic Neurons Innervating the Pineal Gland in Chick: A CTB‐HRP Study

Summary The neurons in bilateral superior cervical ganglia (SCG) innervating the chick pineal gland were labelled by using the technique of retrograde axonal labelling with cholera toxin B subunit linked to horseradish peroxidase (CTB‐HRP). To our results, perikarya of these sympathetic neurons distributed from rostral to caudal in the SCG, and mainly localized in the opposite side of the paravertebral trunk. The fibres of these neurons were collected by the cephalic carotid nerve. According to the sizes of somal area and dendritic field, these sympathetic neurons projecting to the pineal gland were classified into four major groups: group I cells (52.4%) with a small somal area (303.5 μm 2 on average) and narrow dendritic field (3767.8 μm 2 on average), group II cells (39.0%) with a middle‐sized somal area (473.3 μm 2 ) and middle‐sized dendritic field (7522.2 μm 2 ), group III cells (6.4%) with a middle‐sized somal area (473.4 μm 2 ) and wide dendritic field (13 104.4 μm 2 ), and group IV cells (2.2%) with a large somal area (940.7 μm 2 ) and wide dendritic field (14 553.2 μm 2 ). Of these pineal projecting neurons, most took on a lesser dendritic field. The neurons with small or middle‐sized dendritic field from group I and II were about 91.4% of the total neurons labelled with CTB‐HRP, and the neurons with wide dendritic field from group III and IV were less with 8.6%.